The present invention relates to an improved catalyst composition. The catalyst may be used to effect various chemical conversions, and is particularly valuable for use in a process for producing alkylaromatics, particularly ethylbenzene and cumene, or for use in a process for oligomerization of olefins, particularly for production of dimers, trimers and tetramers of olefins, e.g. ethylene, propylene, butylene, or mixtures thereof.
Ethylbenzene and cumene are valuable commodity chemicals that are used industrially for the production of styrene monomer and coproduction of phenol and acetone respectively. Ethylbenzene may be produced by a number of different chemical processes but one process that has achieved a significant degree of commercial success is the vapor phase alkylation of benzene with ethylene in the presence of a solid, acidic ZSM-5 zeolite catalyst. Examples of such ethylbenzene production processes are described in U.S. Pat. No. 3,751,504 (Keown), U.S. Pat. No. 4,547,605 (Kresge), and U.S. Pat. No. 4,016,218 (Haag).
More recently focus has been directed at liquid phase processes for producing ethylbenzene from benzene and ethylene since liquid phase processes operate at a lower temperature than their vapor phase counterparts and hence tend to result in lower yields of by-products. For example, U.S. Pat. No. 4,891,458 (Innes) describes the liquid phase synthesis of ethylbenzene with zeolite Beta, whereas U.S. Pat. No. 5,334,795 (Chu) describes the use of MCM-22 in the liquid phase synthesis of ethylbenzene.
Cumene has for many years been produced commercially by the liquid phase alkylation of benzene with propylene over a Friedel-Craft catalyst, particularly solid phosphoric acid or aluminum chloride. More recently, however, zeolite-based catalyst systems have been found to be more active and selective for propylation of benzene to cumene. For example, U.S. Pat. No. 4,992,606 (Kushnerick) describes the use of MCM-22 in the liquid phase alkylation of benzene with propylene.
Alkylation processes for producing ethylbenzene and cumene in the presence of currently used catalysts inherently produce polyalkylated species as well as the desired monoalkylated product. The polyalkylated species are typically transalkylated with benzene to produce additional monoalkylated product, for example ethylbenzene or cumene, either by recycling the polyalkylated species to the alkylation reactor or, more frequently, by feeding the polyalkylated species to a separate transalkylation reactor having a transalkylation catalyst. Examples of catalysts which have been used in the alkylation of aromatic species, such as alkylation of benzene with ethylene or propylene, and in the transalkylation of polyalkylated species, such as polyethylbenzenes and polyisopropylbenzenes, are listed in U.S. Pat. No. 5,557,024 (Cheng) and include MCM-22, PSH-3, SSZ-25, zeolite X, zeolite Y, zeolite Beta, acid dealuminized mordenite and TEA-mordenite. Transalkylation over a small crystal (<0.5 micron) form of TEA-mordenite is also disclosed in U.S. Pat. No. 6,984,764.
Where the alkylation step is performed in the liquid phase, it is also desirable to conduct the transalkylation step under liquid phase conditions. However, by operating at relatively low temperatures, liquid phase processes impose increased requirements on the catalyst, particularly in the transalkylation step where the bulky polyalkylated species must be converted to additional monoalkylated product without producing unwanted by-products. This has proved to be a significant problem in the case of cumene production where existing catalysts have either lacked the desired activity or have resulted in the production of significant quantities of by-products such as ethylbenzene and n-propylbenzene.
According to the present invention, it has now unexpectedly been found that a specific catalyst manufactured to exhibit a Proton Density Index (“PDI”), as herein defined, of greater than 1.0, for example, from greater than 1.0 to about 2.0, e.g. from about 1.01 to about 1.85, has a unique combination of activity and, importantly, selectivity, especially when used as a liquid phase alkylation catalyst for manufacture of monoalkylated product, particularly for the liquid phase alkylation of benzene to ethylbenzene, cumene or sec-butylbenzene. This obviates or reduces the demand in many instances for the difficult transalkylation reaction for conversion of unwanted bulky polyalkylated species.